Hello TC
Great idea--not sure if would work but first we need ideas. Then...we'll work out the details!

On that parasitic load, your transmission and Engine ECM/ECU are also powered up when you find there is power in the diags socket. That power is being delivered to all the chassis computers. If its on a key switch, then when keys off, all units power down completely. If you're seeing power-on at the jib with the key off, the whole system is live, drawing power...all the time.

The standard for (most all) mfgr's across all years is to key-switch power the computers. Some, from time to time have broke this. Its not a good practice as it ages all the 'CMs prematurely. This includes the VMSpc and TPMS (PressurePro etc) bridge module.